Selective solvent



Unite States Patent SELECTIVE SOLVENT William T. Nelson, Bartlesville,Okla., assignor to Phillips Petroleum Company, a corporation of DelawareNo Drawing. Application June 29, 1953 Serial No. 364,920

27 Claims. (Cl. 252-'1) This invention relates to a novel selectivesolvent for hydrocarbons. In one aspect this invention relates to anovel selective solvent for the separation of different hydrocarbonshaving similar boiling points. In another aspect, it relates to asolvent for the separation of hydrocarbons having difierent carbon tohydrogen ratios. one of its more specific aspects, it relates to anovelselective solvent for the removal of acetylene from a gaseoushydrocarbon mixture containing a minor portion of acetylene. In anotherof its more specific aspects, it relates to a method for the recovery ofacetylene contained as a minor constituent in a gaseous hydrocarbonmixture.

Acetylene may be produced 'by thermal treatment of hydrocarbons by avariety of methods. Among such methods are the treatment of hydrocarbonsof the methane and ethylene series by controlled pyrolysis, passage o f'such hydrocarbons through an electric arc, incomplete combustion, andthe like.

Acetylene is formed as a minor constituent in refinery streams resultingfrom cracking, dehydrogenation and other similar reactions involvingthermal or catalytic treatment of hydrocarbon fractions or petroleumderivatives. These gaseous streams usually contain a relatively smallpercentage of acetylene as compared to the other constituents which maybe present, such as hydrogen, methane, ethylene, ethane, nitrogen, orthe like. A ma- 'jor problem arises in the separation of the severalconstituents of such gaseous mixtures and particularly the concentrationand/ or separation of acetylene.

For the recovery of acetylene from gaseous mixtures, the selectivesolvent action of various compounds and mixtures of compounds have beenused. The most commonly employed solvent is acetone; however, othersolvents such as the dialkyl formamides, the aliphatic lactones, theesters of polyhydric alcohols, the polyketones, and the like have beeneither proposed or used. An ideal solvent for acetylene should have theproperties of high solubility for acetylene, high selectivity foracetylene over the other constituents of the gaseous mixture, highboiling point, high thermal stability, low vapor pressure at ordinarytemperatures and absence of chemical reaction with acetylene or otherconstituents of the gaseous stream. Although the compounds heretoforesuggested for this purpose accomplish acetylene removal and recovery,they do not, in each case, possess all of the above properties and thusthere is considerable room for improvement.

A liquid having high solvent power for acetylene is also important inthe storage of acetylene in pressure retaining vessels. Acetylene iscommonly stored in pressure containers which are partially filled withbalsa wood or other absorbent and porous material into which the solventcontaining dissolved acetylene is introduced under pres sure. The higherthe solvent power of the solvent used, the larger is the volume ofacetylene which may be introduced in the container at a stated pressure,and solvents of high solvent power are therefore desirable.

' one atmosphere partial pressure of solute gas.

The separation of hydrocarbons having similar boiling points presents aproblem. Superfractionation has recently been employed in some of thesedifiicult separations; however, this is usually an expensive process.Fractional crystallization offers another method for the separation ofclose boiling hydrocarbons although this method is likewise expensiveand is time consuming. Another method for such separations is that ofsolvent extraction orextractive distillation and the possibilitiesaiforded by the use of a selective solvent appear to be limited only bythe selectivity and capacity of such solvent and the availability andcost of such'solvent.

Solvent extraction and extractive distillation methods are applicable tothe separation of unsaturated hydrocarbons from less unsaturatedhydrocarbons such as acetylenes from diolefins, diolefins from olefins,olefins from paraflins, and various combinations of the abovehydrocarbon types. The use of solvents is also applicable in theseparation of cycloparafiins (referred to :in the petroleum industry asnaphthenes), from the acrylic paraflins.

'In at least one modification of this invention, at least one of thefollowing objects is attained.

It is an object of this invention to provide a selective solvent foracetylene.

Another object is 'to provide afmethod'jfor the separation ofunsaturated hydrocarbons from less unsaturated hydrocarbons.

Another object is to provide a method for the selective removal andrecovery of acetylene from gaseous mixtures.

Another object 'is to provide a method for the separation ofhydrocarbons having similar boiling points.

Another object is to provide a new composition of matter consisting ofacetylene dissolved in a novel solvent.

It is still another object to provide a selective solvent forunsaturated hydrocarbons in the presence of less unsaturatedhydrocarbons.

It is still another object to provide an improved method for storage ofacetylene.

Other objects will be apparent to one skilled in the art upon readingthis disclosure of the invention.

I have discovered that N-alkyl-Z-pyridones are eifective selectivesolvents for the separation of hydrocarbonshaving ditferent carbon tohydrogen ratios 'but having :similar boiling points. TheN-alkyl-2.-pyridones of this invention are particularly effectiveselective solvents for the separation of acetylene from gaseous mixturescontaining acetylene. The N-alkyl-Z-pyridones are also effectiveselective solvents for the separation of naphthene hydrocarbons such ascyclohexane from the parafiin hydrocarbons having similar boilingpoints, for example, 2,2-dimethyl pentane and 2-4-dimethyl pentane, :andthe separation of aromatics from naphthenes and parafiins.

The solubilities of acetylene and other gaseous con stituents inN-methyl-Z-pyridone are given in Table 'I.

These solubilities are expressed in terms of the Bunsen coeflicient,alpha (or), which is defined as the number of milliliters of solute gas,calculated at 760 millimeters of pressure and 0 C., dissolved permilliliter of solvent at The selectivities (ratio of solubilities) ofN-methyl-Z-pyridone for acetylene over ethylene and for acetylene overcarbon dioxide are given in Table H.

4 The N-alkyl-Z-pyridones applicable in the practice of my invention arethose wherein the alkyl radical contains Data showing the selectivitiesof N-methyl-Z-pyridone for benzene over n-heptane and for cyclohexaneover n-heptane are presented in Table III.

The data in Tables I, II, and III were obtained at atmospheric pressureand the indicated temperatures.

The novel solvents of my invention possess physical properties whichmake them very useful as solvent for acetylene. Some of these propertiesare given in Table IV.

TABLE IV Properties of solvents Solvent N-methyl- N-ethyl- N-isopropyl-2-pyrldone 2-pyridone 2-pyridone Molecular weight 109 123137. Boiling point, 250 249-250 145-150 (at mm. Hg). Vapor pressure, at1 1 80 0.. mm. Freezing point, O

In an acetylene recovery process, the acetylene-containing effiuentstream is subjected to countercurrent scrubbing in any suitableabsorbent tower, such as a spray, packed, or bubble plate tower. Thesolvent need not be a pure compound and may be admixed with otheracetylene solvents or liquid materials which have no selective solventaction on acetylene. The temperatures and pressures employed may varyover Wide limits but very often ordinary temperatures and pressures areused. It is preferred to operate at a temperature substantially belowthe boiling point of the solvent and above the dew-point of the gaseousmixture at the existing pressure. At very low temperatures, for a fixedpressure, the solubility of acetylene is increased, but the solubilityfor other gases may be so great that lower selectivity is obtained;whereas, at high temperatures so little acetylene may be dissolved, thatselectivity is of little consequence. The use of superatmosphericpressure improves the capacity of the solvent for acetylene but requiresmore expensive equipment. The acetylene selectively absorbed in thesolvent along with small amounts of other gases is recovered by eitherheating the solution to expel the gas, reducing the pressure over thesolution to effect a separation of the dissolved gas, or-by using acombination of both features. Thereafter, the solvent is recirculated inthe system.

I prefer to use N-methyl-Z- the propyl and less than 5 carbon atoms.pyridone and N-ethyl-Z-pyridone; however, butyl derivatives can also beused.

The naphthenes which can be separated from mixtures of naphthenes andparaffins include cyclopentane, cyclobutane, methylcyclopentane,ethylcyclopentane, methylethylcyclopentane, methylcyclohexane,ethylcyclohexane, methylethylcyclohexane, cycloheptane, andthe like. Thearomatics which can be separated from mixtures of hydrocarbonscontaining aromatics include toluene, ethylbenzene, xylenes, isopropylbenzene, tert-butyl benzene, and the like. Olefins such as ethylene,propylene, butene, etc. can be separated from paraffins by the practiceof this invention.

I prefer the practice of the separation process of my invention upongaseous hydrocarbons; however, the invention is also applicable toliquid hydrocarbons. In theseparation of liquid hydrocarbons havingsimilar boiling points, known solvent extraction and/or extractivedistillation processes can be employed.

Variations and modifications are possible within the scope of thedisclosure of the present invention, the essence of which is thatN-alkyl-Z-pyridones have been discovered to be effective selectivesolvents for separating hydrocarbons having different carbon to hydrogenratios and particularly for separating acetylene from olefins andparaflins.

I claim:

1. The process of separating an unsaturated hydrocarbon selected fromthe group consisting of acetylenes, aromatic hydrocarbons, and naphthenehydrocarbons from a less unsaturated hydrocarbon selected from the groupconsisting of olefins, aromatic hydrocarbons, naphthene hydrocarbons,and parafiin hydrocarbons which comprises contactingsaid hydrocarbonswith a N-alkyl- Z-pyridone having less than 5 carbon atoms in the alkylradical and separating said N-alkyl-2-pyridone containing dissolvedunsaturated hydrocarbon from the remaining less unsaturated hydrocarbon.7

2. The process of claim 1 wherein the unsaturated hydrocarbon isacetylene and the less unsaturated hydrocarbon comprises ethylene,ethane, and methane in a gaseous mixture.

3. The process of claim 1 wherein the unsaturated hydrocarbon is anolefin and the less unsaturated hydrocarbon comprises paratfins andnaphthenes.

4. The process of claim 1 wherein the N-alkyl-Z- pyridone isN-methyl-2-pyridone.

5. The process of claim 1 wherein the N-alkyl-Z- pyridone isN-ethyl-Z-pyridone.

6. The process of claim 1 wherein the N-alkyl-2- pyridone isN-isopropyl-Z-pyridone.

of acetylene dissolved in a N-alkyl-2-pyrid0ne having less than 5 carbonatoms in the alkyl radical.

10. The composition of claim 9 wherein the N-alkyl- 2-pyridone isN-methyl-Z-pyridone. i

12. The composition of claim 9 wherein the N-alkyl- 2-pyridone isN-isopropyl-Z-pyridone.

13. A package which comprises a pressure resistant container, anadsorbent material, a N-alkyl-Z-pyridone having less than 5 carbon atomsin the alkyl radical, and acetylene.

14. The Z-pyridone 15. The 2-pyridone package of claim 13 wherein theN-alkylis N-methyl-Z-pyridone.

package of claim 13 wherein the N-alkylis N-ethyl-Z-pyridone.

16. The package of claim 13 wherein the N-alkyl- Z-pyridone isN-isopropyl-Z-pyridone.

17. A method for the storage of acetylene which comprises dissolvingacetylene in a N-alkyl-2-pyridone having less than 5 carbon atoms in thealkyl radical and confining a resulting solution in a storage zone.

18. The process of purifying an ethylene stream containing acetylene asan impurity which comprises contacting said ethylene stream in thegaseous phase with a N-alkyl-Z-pyridone having less than 5 carbon atomsin the alkyl radical.

19. The process of removing aromatic hydrocarbons from a hydrocarbonmixture containing aromatic hydrocarbons which comprises contacting saidmixture with a N-alkyl-Z-pyridone having less than 5 carbon atoms in thealkyl radical and removing said N-alkyl-Z-pyridone solvent containingsaid aromatic hydrocarbon dissolved therein.

20. The process of separating naphthene hydrocarbons from a mixturecontaining naphthene hydrocarbons and paraffin hydrocarbons whichcomprises contacting said mixture with a N-alkyl-Z-pyridone having lessthan 5 carbon atoms in the alkyl radical and removing saidN-alkyI-Z-pyridone solvent containing naphthene hydrocarbon dissolvedtherein.

21. The process of claim 19 wherein pyridone is N-methyl-Z-pyridone.

22. The process of claim 19 wherein pyridone is N-ethyl-Z-pyridone.

23. The process of claim 19 wherein pyridone is N-isopropyl-Z-pyridone.

24. The process of claim 20 wherein pyridone is N-methyl-Z-pyridone.

25. The process of claim 20 wherein pyridone is N-ethyl-Z-pyridone.

26. The process of claim 20 wherein pyridone is N-isopropyl-Z-pyridone.

27. The process of removing acetylene from a gaseous mixture containingacetylene and carbon dioxide which comprises contacting said mixturewith an N-alkyl-2- pyridone having less than 5 carbon atoms in the alkylradical.

the N-alkyl-2- the N-alkyl-2- the N-alkyl-Z- the N-alkyl-Z- theN-alkyl-2- the N-alkyl-Z- References Cited in the file of this patentUNITED STATES PATENTS 2,405,693 Hamill et al. Aug. 13, 1946 2,431,675Bour Dec. 2, 1947 2,599,649 Lorenz June 10, 1952 2,664,997 Eck Jan. 5,1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N002,849,396 Augu st 26, 1958 William To Nelson printed speeifieation It ishereby certified. that error appears in the that the said Letters of theabove numbered patent requiring correction and, Patent should. read ascorrected belowo Column 2, line 20, for "acrylic" reed acyclic, ==o

Signed and sealed this 27th day of January 19590 f em Attest: 5

KARL MINE i ROBERT c. WATSON commissioner of Patents 7 Attesting-Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIDN Augu st26, 1958 Patent No, 2,849,396

William T Nelson 5 'in the printed epeeifieation.

It is hereby certified that error appear tion and. that the said Lettersof the above numbered patent requiring; eorreo Patent should read ascorrected belowo Column 2, line 20;, for "acrylic" read aeyelie Signedand sealed this 27th day] of Jrmuary 19590 r em) Attest:

KARL HAXLINE ROBERT c. WATSON Comissioner of Patents Attesting; Officer

1. THE PROCESS OF SEPARATING AN UNSATURATED HYDROCARBON SELECTED FROMTHE GROUP CONSISTING OF ACETYLENES, AROMATIC HYDROCARBONS, AND NAPHTHENEOF ACETYLENES, FROM A LESS UNSATURATED HYDROCARBON SELECTED FROM THEGROUP CONSISTINGOF OLEFINS, AROMATIC HYDROCARBONS NAPHTHENEHUDROCARBONS, AND PARAFFIN HYDROCARBONS WHICH COMPRISES CONTACTING SAIDHYDROCARBONS WITH A N-ALKYL2-PYRIDONE HAVING LESS THAN 5 CARON ATOMS INTHE ALKYL RADICAL AND SEPARATING SAID N-ALKYL-2-PYRIDONE CONTAININGDISSOLVED UNSATURATED HYDROCARBON FROM THE REMAINING LESS UNSATURATEDHYDROCARBON.
 13. A PACKAGE WHICH COMPRISES A PRESSURE RESISTANTCONTAINER, AN ADSORBENT MATERIAL, A N-ALKYL-2-PYRIDONE HAVING LESS THAN5 CARBON ATOMS IN THE ALKYL RADICAL, AND ACCETYLENE.